Field of the Invention
The present invention relates to a solid-state imaging device and an imaging system.
Description of Related Art
In recent years, imaging systems, such as video cameras or electronic still cameras, have become widespread. In these imaging systems, a charge-coupled device (CCD) type solid-state imaging device or a complementary metal oxide semiconductor (CMOS) type solid-state imaging device is mounted. In these solid-state imaging devices, a plurality of pixels are arranged in a two-dimensional matrix, and signal charges generated by a photoelectric conversion unit such as a photodiode provided in a pixel on which light is incident are amplified by an amplifier provided in the pixel and are output as a pixel signal. In this case, in a general CMOS type solid-state imaging device, pixel signals from the pixels arranged in a two-dimensional matrix are sequentially read in each row.
A CMOS type solid-state imaging device can be manufactured using a general semiconductor manufacturing process, while a CCD type solid-state imaging device can be manufactured by a dedicated manufacturing process. Accordingly, in a CMOS type solid-state imaging device, it is easy to realize multiple functions by providing various functional circuits in the solid-state imaging device, for example, as in a system-on-chip (SOC). For this reason, in a CMOS type solid-state imaging device (hereinafter, referred to as a “solid-state imaging device”) mounted in an imaging system, the number of examples of using a solid-state imaging device having a configuration in which an analog-to-digital conversion circuit is provided and pixel data obtained by performing analog-to-digital conversion of a pixel signal read from each pixel is output has increased.
There are various operation modes in an imaging system. Therefore, the solid-state imaging device has a structure capable of outputting pixel data with the number of pixels suitable for the operation mode of the imaging system by performing pixel addition for summing the pixel signals read from the pixels or thinning-out reading for thinning out and reading the pixel signals of the pixels according to the operation mode of the imaging system (refer to Japanese Unexamined Patent Application, First Publication No. 2008-199177). An image-processing unit provided in an imaging system generates an image, which has a size corresponding to each operation mode of the imaging system, based on the pixel data of the various numbers of pixels that is output from the solid-state imaging device.
For example, in the case of an operation mode to capture a still image in an imaging system including a solid-state imaging device in which 5760 pixels (in the horizontal direction) by 4320 pixels (in the vertical direction) are arranged, the solid-state imaging device outputs pixel data of all pixels (5760 pixels×4320 pixels). Then, the image-processing unit generates a still image having 5760 pixels×4320 pixels by performing image processing on the pixel data of all pixels output from the solid-state imaging device, and records the still image. In the case of an operation mode to capture a moving image in an imaging system, the solid-state imaging device outputs pixel data obtained by performing pixel addition or thinning-out to the same number of pixels (1920 pixels×1080 pixels) as the 1080P format that is mainstream in current moving image capturing, for example. Then, the image-processing unit generates a moving image having 1920 pixels×1080 pixels by performing image processing on the pixel data output from the solid-state imaging device, and records the moving image. In the case of an operation mode to output a check image (so-called live view image (through image)) for checking a subject in the imaging system, the solid-state imaging device outputs pixel data obtained by performing pixel addition or thinning-out to the same number of pixels (1920 pixels×1440 pixels) as the number of pixels that can be displayed on a display device, such as a liquid crystal display (LCD), for example. Then, the image-processing unit generates a live view image having 1920 pixels×1440 pixels by performing image processing on the pixel data output from the solid-state imaging device, and outputs the live view image.
The reason why the number of pixels of pixel data output from the solid-state imaging device is changed according to the operation mode of the imaging system as described above is that the size of an image, which is finally output from the imaging system, or a delay (real-time performance) until an update is completed changes according to the operation mode. That is, in the case of an operation mode in which the imaging system captures a still image, priority is given to the number of pixels over the real-time performance in order to ensure the quality of a still image to be generated, so that pixel data with a large number of pixels is output from the solid-state imaging device. In contrast, in the case of an operation mode in which the imaging system captures a moving image or an operation mode in which the imaging system outputs a through image, priority is given to the real-time performance over the number of pixels so that the movement of a subject included in a moving image or a through image to be generated is smooth. As a result, pixel data with the number of pixels, which has been reduced to a size that meets the standards by pixel addition or thinning-out, is output from the solid-state imaging device with a high real-time performance.
In an imaging system, there is also processing performed according to the overall state of an image to be captured, for example, control for performing imaging, such as auto exposure (AE), auto focus (AF), and auto white balance (AWB), or image recognition processing for detecting the movement or face of a subject included in the captured image. These processes can ensure accuracy even in a case where processing is performed using a small-size image. For this reason, in these processes, large-size pixel data output from the solid-state imaging device is not required, and a high real-time performance is strongly required instead. That is, in these processes, the number of pixels may be further reduced from that in the operation mode to capture a moving image or the operation mode to output a through image, but outputting pixel data from a solid-state imaging device with a higher real-time performance is required.
The control, such as AE, AF, and AWB, or the image recognition processing described above is performed in parallel with the capturing of a still image or a moving image or in parallel with the output of a through image. For this reason, in the image-processing unit provided in the imaging system, pixel data input from the solid-state imaging device for the generation of a still image or a moving image or for the output of a through image is converted to a size suitable for each process performed in the imaging system. For example, the image-processing unit converts the size of pixel data output from the solid-state imaging device to the number of pixels of 640 pixels×480 pixels in order to use the pixel data in the control, such as AE, AF, and AWB, or the image recognition processing. Accordingly, each processing unit can perform the processing it is in charge of based on the size-converted pixel data.
Thus, although the size of pixel data required for each process is different in the imaging system, the size of pixel data output from the solid-state imaging device is converted to a size suitable for each process by the image-processing unit.